it occured to me that the reason I dislike a character at first but then don't later has to do the way I read.

When I'm reading a book for the first time, a lot of my gut reactions on characters come out. I react to the character and the way it interacts in the story.

Second time around though, i analyse. I look at why characters are built the way they are and what role they play in the story. Also, having already read thew story, i see their actions as a whole rather than just to that exact moment.